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Figure 4 | Earth, Planets and Space

Figure 4

From: Small-scale stress fluctuations in borehole breakouts and their implication in identifying potential active faults around the seismogenic megasplay fault, Nankai Trough, SW Japan

Figure 4

Stress magnitudes (left), breakout orientations (center), and fractures (right) identified at C0004B. The magnitude of S V may be smaller than that of S Hmax but within the possible range of S hmin, suggesting that the stress around this borehole would be in a reverse fault or strike-slip fault regime. The plot of breakout orientations with depth, measured from the north, shows that the two breakouts at the same depth are roughly 180° apart even where the direction of the breakouts fluctuates, suggesting that the fluctuations of breakout orientation are produced by systematic rotations. The heavily fractured zones with a high fracture frequency (Yamada et al. 2011) are within the megasplay fault zone and its hanging wall and generally correspond to the intervals of anomalous rotations of the breakouts and the decreases in stress magnitude. The arrows indicate possible active faults suggested by rotated and decreased stresses. APRS is the average annular pressure.

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